1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and a method of detecting a toner state, more particularly to an image forming apparatus configured to detect a toner almost empty state or a toner empty state or neither, accommodated in a toner supplying unit and a method of detecting the toner state in the image forming apparatus.
2. Discussion of the Related Art
In an image forming apparatus using a two-component developer in which toner and carrier are mixed, as a developing unit consumes more toner for image forming, an image density of a printed image becomes lower. A toner density sensor that is disposed in the developing unit detects a toner density, and toner is accordingly supplied from a toner supplying unit or a toner cartridge to the developing unit when the toner density becomes low, so that the toner density in the developing unit may constantly be maintained within the appropriate range.
When toner remaining in the toner supplying unit becomes almost or completely empty, the toner supplying unit may need to be replenished with toner.
To allow time to obtain a new toner supplying unit or toner cartridge, it is preferable that a warning that the toner is becoming empty or a message indicating a toner almost empty state be displayed when the toner supplying unit still holds an amount of toner for printing some dozens of images.
There are some techniques to detect the toner almost empty state of the toner remaining in the toner supplying unit. In one technique, for example, a sensor is used to detect a torque of a toner agitator mounted in the toner supplying unit. When the torque becomes below a predetermined level, the toner almost empty state is displayed. However, the detection accuracy of torque may gradually decrease when the amount of remaining toner in the toner supplying unit becomes lower.
A background image forming apparatus for detecting and accurately determining a toner empty state in a toner supplying unit includes an optical writing unit for forming an electrostatic latent image, a developing unit for developing the electrostatic latent image, a toner accommodating unit for accommodating toner to be supplied to the developing unit, a plurality of toner containers detachable with respect to the toner accommodating unit for containing the toner to be supplied to the toner accommodating unit, a remaining toner detecting unit for detecting the amount of remaining toner in the toner container, and a development ability detecting unit for detecting ability of the developing unit. The above-described image forming apparatus further includes a toner almost empty state determining unit for determining a toner almost empty state based on the detection result that the toner in the toner container becomes completely or almost empty, and a toner empty state determining unit for determining a toner empty state based on the image data of an image to be formed after the toner almost empty state is determined by the toner almost empty state determining unit and the detection result of development ability obtained by the development ability detecting unit.
A different background image forming apparatus uses a dot counter and a toner density sensor in detecting the toner almost empty state and the toner empty state for achieving simplification as well as cost reduction of the background image forming apparatus. The image forming apparatus includes the dot counter for counting the number of dots of a formed image, a developing unit including the toner density sensor, a laser writing unit, and a detecting unit for detecting the toner almost empty state according to the result value of the dot counter and detecting the toner empty state according to the result of the toner density sensor.
A different background image forming apparatus employs a photoelectrical sensor or a P-sensor. The P-sensor is widely used to detect the density of developer so that the image density can be maintained in a constant range.
In this image forming apparatus, an electrostatic latent image of a reference density pattern is formed on a surface of an image bearing member of the image forming apparatus, by scanning the reference density pattern that is provided at a lower position of a side scale on a contact glass of the image forming apparatus or by scanning the image bearing member by a laser light beam that repeatedly blinks at a constant interval of time. The developing unit develops the electrostatic latent image of the reference density pattern to form a visible pattern. The P-sensor detects the toner density of the visible pattern and the toner density of the background area of the image bearing member in a unit of voltage.
The toner density detection may be performed after printing every 10 copies, for example. For example, when a the Vsp/Vsg value becomes equal to or less than 1/10, in which “Vsp” represents a voltage corresponding to the toner density of the visible pattern and “Vsg” represents a voltage corresponding to the toner density of the background area of the image bearing member, the P-sensor determines whether the ratio of toner in the developer has fallen below the predetermined amount. Then, the toner supplying unit supplies toner to the developing unit continuously until the Vsp/Vsg value becomes greater than 1/10.
Referring to FIGS. 1 and 2, flowcharts of background operations for detecting toner states are described.
FIG. 1 shows the operation flowchart of a toner almost empty detecting check of a background image forming apparatus.
A toner empty sensor serving as an optical detecting unit is disposed in a toner conveying path. The toner empty sensor determines whether the toner almost empty state of a toner supplying unit has been detected in step S1.
When the toner empty sensor has detected the toner almost empty state (YES in step S1), the image forming apparatus sets a toner almost empty flag and shows a toner almost empty signal to inform a user of the toner almost empty state in step S2.
Even when the toner empty sensor has not yet detected the toner almost empty state (NO in step S1), the image forming apparatus obtains a difference between a target toner density (Vref) and the current toner density (Vt) in step S3.
When the difference exceeds a predetermined value, 0.4V for example, continuously for a given number “n” of transfer sheets (YES in step S3), the process goes to step S2 so as to set the toner almost empty flag and show the toner almost empty signal.
When the difference stays 0.4V or below (NO in step S3, the toner almost empty flag is left unset in step S4.
FIG. 2 shows the operation flowchart of a toner empty detecting check of the background image forming apparatus.
The toner empty sensor determines whether the toner almost empty state of the toner supplying unit has been detected in step S11.
When the toner empty sensor has detected the toner almost empty state (YES in step Sll), the image forming apparatus determines whether a specific number of pixels has been output in step S12.
When the specific number of pixels has been output (YES in step S12), the image forming apparatus sets a toner empty flag and shows a toner empty signal to inform a user of the toner empty state in step S13.
Even when the toner empty sensor has not yet detected the toner almost empty state (NO is step S11), the image forming apparatus obtains a difference between a target toner density (Vref) and the current toner density (Vt) in step S14.
When the difference exceeds a predetermined value, 0.5V for example, continuously for a given number “n” of transfer sheets (YES in step s14), the process goes to step S13 so as to set the toner empty flag and show the toner empty signal.
When the difference stays 0.5V or below (NO in step s14), the toner empty flag is left unset in step S15.
When a small amount of toner remains in the toner supplying unit, however, the replenishment of sufficient toner cannot be supplied to the developing unit even though instructions for supplying toner are repeatedly sent, and the toner density of image pattern area cannot recover to the predetermined acceptable range. When the above-described situation occurs, the toner empty sensor determines the toner almost empty state and the warning is displayed on a console or a message window.
As previously described, the P-sensor determines the toner almost empty state according to the toner density of a visible pattern. Therefore, when images having high image area coverage are continuously formed or when the potentials are varied, the toner almost empty state may be detected and the toner almost empty signal may be consequently displayed even when the toner is sufficiently contained in the toner supplying unit. In this case, the entire system is caused to stop, which has caused the toner contained in the toner supplying unit not to be effectively used until the end of toner.
Further, an optically transparent material is used for a portion of the toner conveying path in the toner supplying unit so as to detect the amount of remaining toner in the toner supplying unit according to the amount of transmitted light. However, the detection accuracy may degrade when a portion of the toner conveying path is contaminated.
Further, a magnetic permeability sensor is used for detecting the toner density in a two-component developer so as to calculate the difference between the toner density and a target toner density. When the difference exceeds a predetermined level, the toner in the toner supplying unit is determined to be in the toner almost empty state.
However, when the image area coverage of output image sharply increases or decreases or when the environmental condition around the image forming apparatus greatly changes, the volume of the developer may change. The magnetic permeability sensor can cause erroneous detections of the toner under the above-described condition. Especially, when images having high image area coverage are sequentially output, the detection level of density of the sensor may shift to a lighter level.